A toner hopper has been known as a developer cartridge for accommodating toner. One type of toner hopper is freely detachably mounted onto a main body of an image forming device. This type of toner hopper includes a hopper frame and a cover. The hopper frame accommodates toner therein and is formed with a communication hole through which the toner is supplied to the main body side of the image forming device. The cover selectively opens and closes the communication hole.